1. Field of the Invention
The present invention relates to a magnetic bearing device having an actuator function and a sensing function, and a vacuum pump having such a magnetic bearing device.
2. Description of the Related Art
In a known constitution for vacuum pumps provided with a magnetic bearing device, in order to realize downsizing, price reduction, and reliability improvement, a position sensor for detecting levitation displacement of a rotor is not provided, and an electromagnet for generating a levitation controlling force serves a sensing function in addition to a conventional actuator function (see JP 2009-275740 A, for example).
In a conventional magnetic bearing device, an excitation current is supplied by applying a switching voltage from a PWM amplifier to an electromagnetic coil. In a magnetic bearing device having an actuator function and a sensing function, levitation position information of a rotor is obtained by detecting the electromagnetic current. When switching, as a spike-like noise due to a surge voltage or the like is produced in the electromagnetic current, a magnetic bearing device described in JP 2009-275740 A takes timing for sampling of a current at a middle point of voltage switching.
However, when on-duty is around 0% or around 100% in PWM control, next switching timing comes before a switching noise attenuates sufficiently. In such a case, even if the sampling is performed at a middle point in the voltage switching, an influence of a switching noise to the sampling is inevitable.